1. Field of the Invention
The present invention relates to an image forming apparatus which performs printing with a transparent recording agent serving as a spot color recording agent.
2. Description of the Related Art
Recently, an image processing apparatus capable of printing with a transparent toner (i.e., clear toner) has been discussed. The transparent toner is one of the spot color recording agents.
A whole surface coating is obtained by printing a transparent toner on an entire printable area of a print sheet. Such a whole surface coating can provide the entire sheet surface with glossiness like a photograph by printing the sheet with color toners such as cyan, magenta, yellow, and black (CMYK) toners and then printing the entire sheet with the transparent toner. A partial coating, on the other hand, is obtained when a print sheet is printed with color toners, and then a designated area in a printable area of the print sheet is printed with a transparent toner. The partial coating can provide the sheet with partial glossiness or a partial decoration effect. When such a transparent toner is used in printing, therefore, various expressions can be obtained, thereby generating a value-added output product.
Further, so as to perform printing with the transparent toner, an image processing apparatus may include a mechanism for fixing color toner images and a transparent toner image onto a sheet in a single fixing process, after CMYK toners serving as color toners and a transparent toner are transferred to the sheet. Accordingly, the image processing apparatus can generate an output product using the transparent toner.
However, the addition of such a mechanism for printing with the transparent toner may cause, for example, a problem of a loaded amount of the toner. More specifically, the image processing apparatus has limitation on a toner amount, which can be fixed at a single fixing process in per unit area of a print target sheet (limitation on loaded amount). Consequently, an area in need of a large amount of color toners cannot be provided with a sufficient amount of the transparent toner to suppress a toner amount within the limitation of loaded amount.
Accordingly, Japanese Patent Application Laid-Open No. 2008-145595 discusses an image processing system for generating an output product using a transparent toner by connecting an image processing apparatus that uses color toners in printing and an image processing apparatus that uses a transparent toner in printing. For example, a user who uses a transparent toner is offered to use an image processing system in which an image processing apparatus in a previous stage is connected to another image processing apparatus in a latter stage. The image processing apparatus of the previous stage performs printing by transferring and fixing color toners, whereas the image processing apparatus of the latter stage performs printing by transferring and fixing a transparent toner. According to such a configuration, both of the color toners and the transparent toner can be used sufficiently with respect to a print target.
In addition, effects on output products can be varied depending on types of print sheets to be used. For example, use of a transparent toner does not always provide an output product surface with the glossy expression, and there are cases where a surface of an output product can have a matte expression by using the transparent toner. In other words, when a transparent toner is used, a surface texture of an output product can be changed. The glossy expression attained with use of the transparent toner is referred to as a “gloss effect”, whereas the matte expression is referred to as a “matte effect”. These two effects are referred to as “effects relating to glossiness”. A user needs to perform complicated settings at the time of printing to obtain such effects. The complicated settings, for example, include selection of a sheet type to be used in printing and selection of a printing method of a transparent toner. Consequently, the user has a difficulty in dealing with the settings.
Japanese Patent Application Laid-Open No. 2009-265405 discusses an image processing apparatus capable of automatically selecting a sheet type and a printing method when a user sets an effect relating to glossiness to be expressed on a desired area on a print sheet.
An effect attained with use of the transparent toner is not limited to the above-described effect relating to glossiness. For example, when a transparent toner is printed on an area with color toners printed thereon, the print area can be finished with a pearl tone. An effect for adding such a pearl tone finish to a printing area using the transparent toner is referred to as a pearl effect. The pearl effect is obtained when the transparent toner is added to an area in which a color toner having a low density is printed.
As described above, the transparent toner can be printed by two methods, a printing method for fixing color toner images and a transparent toner image on a sheet in a single fixing process, and a printing method for fixing color toner images on a sheet and then fixing a transparent toner image on the sheet.
Compared to these two methods, the printing method, which can fix the color toner images and the transparent toner image at once, can equally apply heat to the transparent toner image and the color toner images, so that the toners are well mixed. When a pearl effect is to be obtained, it is desirable that color toners and a transparent toner may be uniformly mixed. In other words, the color toners and the transparent toner may be fixed together at once to obtain the pearl effect.
When the transparent toner is used in printing to express the pearl effect, therefore, a density of the color toners serving as background of the transparent toner and a fixing method at the time of printing of the transparent toner need to be considered. Moreover, it may be a heavy burden for a user to perform settings for realizing the pearl effect.